The present invention relates to the field of precast concrete insulated sandwich panels in which the exterior wythes of concrete sandwich a singular interior wythe of insulation. The tie shear connection of this invention functions to connect the two concrete wythes structurally so as to form a singular structural wall panel that acts as a composite singular wall element. The invention transfers loads (such as wind) imposed onto one concrete wythe across the insulation layer and into the opposite concrete wythe. These two concrete wythes act in concert (composite action) to provide a singular load-resisting element greater than the sum capacities of the individual wythes.
An insulated sandwich panel is composed of two layers (wythes) of concrete separated by a high density foam insulation in the center. The thickness of the concrete layers varies depending upon the structural requirements of the building. The most common load requirements include wind load, roof load, and seismic load. These loads must be collected and then transferred to the building frame and the building foundation. The two concrete wythes handle the majority of this work in concert. But, when the concrete layers are separated by an insulation layer, a structural tie must be used to connect the two concrete wythes together across the insulation layer in such a manner as to cause the two concrete wythes to function more as a single composite unit structurally. However, conventional ties allow thermal bridging, or a loss of heating/cooling energy via the structural tie.
There is an initial bond between the concrete and insulation, but this bond is eventually broken due to handling, temperature differentials and cycling, or service loads, it is necessary to provide shear connectors to transfer forces between the wythes due to longitudinal bending of a panel. These connectors have sufficient strength and stiffness to allow a significant level of interaction between the wythes in the resistance of loads. Non-shear connectors are not designed to transfer longitudinal shear forces between the wythes and primarily serve as a means to hold the various layers together. Traditionally, steel inserts or solid concrete penetrations through the insulating layer have been the primary means of shear connection. These connectors, however, result in thermal short-circuits across the insulation layer and decrease the thermal efficiency of the panel. Steel inserts can also lead to unsightly oxidation or rust on the panel faces.
In an effort to eliminate the problem of thermal bridging, the use of fiber reinforced plastic (FRP) materials in the fabrication of wythe connectors, such as dowel pin connectors and bent bar connectors, was started. With a thermal conductivity approximately 1/100 that of stainless steel, FRP material is seen as an excellent replacement for steel or concrete as wythe connectors. However, FRP dowel pin connectors are inserted normal to the layers. Thus, they have glass fibers subjected to bending during loading of the sandwich panel. The load capacity of the pins is resin-dependent. Many more pins are typically required to replace a few steel trusses.
Therefore, a primary objective of the present invention is the provision of an improved structural shear tie connector.
A further objective of this invention is the provision of an essentially thermally non-conductive (non-metallic) shear tie connector having transverse webs wherein the angled members are in tension under loading conditions.
A further objective of this invention is the provision of a tie connector that is strong, compact, economical to manufacture, and easy to install.
These and other objectives will become apparent from the drawings, as well as from the description and claims which follow.